Echo cancellation device, non-transitory computer readable medium storing echo cancellation program, and echo cancellation

ABSTRACT

An echo cancellation device includes an echo signal reduction processing unit that generates a transmitting signal in which an echo signal component is reduced from the acoustic signal; and a filter coefficient update determination unit that instructs the echo signal reduction processing unit to update the filter coefficient when the output voice signal corresponds to a voice section and the acoustic signal includes the echo signal component. The filter coefficient update determination unit calculates a feature value of the acoustic signal and instructs to update the filter coefficient when a difference between a first feature value of a frequency band equal to or lower than the target frequency and a second feature value of a frequency band higher than the target frequency is equal to or greater than a preset update determination threshold.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a bypass continuation of PCT/JP2015/004520 filed on7 Sep., 2015 which is based upon and claims the benefit of priority fromJapanese patent application No. 2014-206855, filed on Oct. 8, 2014, thedisclosure of each is incorporated herein in its entirety by reference.

BACKGROUND

The present invention relates to an echo cancellation device, an echocancellation program, and an echo cancellation method, and moreparticularly, to an echo cancellation device, an echo cancellationprogram, and an echo cancellation method which reduce echo signalcomponents generated when a voice signal output from the echocancellation device is input through a microphone of the echocancellation device.

In recent years, hands-free communication devices have been used in manycases as auxiliary devices for making a call without the need to hold acommunication device, such as a cellular phone, in a user's hand. Thehands-free communication devices are grouped into a head set type inwhich a headset that is a combination of an earphone and a microphone isconnected to a cellular phone or the like, and a speaker type in which aloudspeaker and a microphone are connected to a cellular phone or thelike. Among the hands-free communication devices, the hands-freecommunication device of the type using a loudspeaker and a microphoneprevents a cable or the like from getting entangled with a user.Accordingly, this type of hands-free communication device isparticularly suitable for use in driving an automobile or the like.

However, in the speaker-type hands-free devices, a voice signaltransmitted from the loudspeaker comes into the microphone, so that anecho to be transmitted to a call destination is generated. If an echo isgenerated during a call, the voice signals resonate with each other andthe clarity of a speech may deteriorate, or howling may occur, whichmakes it difficult to continue the call. Techniques for improving theclarity of a speech by solving the problem of echo and the like aredisclosed in, for example, Japanese Unexamined Patent ApplicationPublication No. H07-221832 and Japanese Unexamined Patent ApplicationPublication No. 2011-130170.

Japanese Unexamined Patent Application Publication No. H07-221832discloses a frequency characteristic control method for obtaining asufficient clarity of a speech even when the level of ambient noise ishigh. In Japanese Unexamined Patent Application Publication No.H07-221832, frequency spectrums of a transmitting acoustic signal and anincoming acoustic signal are detected. In accordance with the magnitudeof a level difference between the frequency spectrums, the incoming callfrequency spectrum is set to be equal to or higher than the level of anoise frequency spectrum in a frequency range equal to or higher than alower-limit frequency necessary for obtaining a clarity of a speech of70% or more. When a maximum level difference between the noise frequencyspectrum and the incoming call frequency spectrum is equal to or lowerthan a predetermined limit value, the component level of the incomingcall frequency spectrum lower than the required lower-limit frequency isincreased according to the amount of component level change. When themaximum level difference exceeds the predetermined limit value, thecomponent level of the incoming call frequency spectrum lower than therequired lower-limit frequency is reduced, and at the same time, thecomponent level of the incoming call frequency spectrum equal to orhigher than the required lower-limit frequency is increased.

Japanese Unexamined Patent Application Publication No. 2011-130170discloses an echo canceller that removes an echo. The echo cancellerdisclosed in Japanese Unexamined Patent Application Publication No.2011-130170 includes: specific frequency component removing means foroutputting, to an echo path, a signal in which a specific frequencycomponent of a specific frequency is removed from a received signal;specific frequency component detection means for detecting, from atransmitting signal, a frequency component having the same frequency asthe specific frequency removed by the specific frequency componentremoving means; noise calculation means for obtaining noise power basedon the power of the specific frequency component detected by thespecific frequency component detection means, and obtaining a totalpower including noise and an echo component on the basis of the power offrequency components including the echo component; and control parametercalculation means for obtaining a control parameter for the echocanceller by using the noise power and the total power obtained by thenoise calculation means.

SUMMARY

However, the technique disclosed in Japanese Unexamined PatentApplication Publication No. H07-221832 has a problem that the noisecomponent and the echo signal component cannot be separated from eachother, which makes it difficult to reduce the echo. Further, as thetechnique disclosed in Japanese Unexamined Patent ApplicationPublication No. 2011-130170 has a problem that the voice componentemitted from the speaker is included in the noise power in a double-talkstate in which a speaker emits a voice at the same time a transmittingsignal is output, it is difficult to accurately detect the echocomponent and leads to deterioration in the effect of echo cancellation.In other words, the use of the techniques disclosed in JapaneseUnexamined Patent Application Publication No. H07-221832 and JapaneseUnexamined Patent Application Publication No. 2011-130170 may beinsufficient for obtaining an effect of suppressing the echo signalcomponent, which makes it difficult to sufficiently increase the qualityof a call.

Accordingly, this embodiment provides an echo cancellation deviceincluding: a voice output unit configured to output, to a space, anoutput voice signal in which frequency components equal to or higherthan a predetermined target frequency are suppressed, as a first voicesignal; a voice input unit configured to pick up a second voice signalpropagating through the space and generate an acoustic signal includinga frequency component higher than the target frequency; a delayprocessing unit configured to delay the output voice signal; a voicesection detection processing unit configured to detect that the outputvoice signal delayed by the delay processing unit corresponds to a voicesection including a voice signal component, and generate voice sectioninformation; a filter coefficient update determination unit configuredto determine whether or not the acoustic signal includes an echo signalcomponent corresponding to the output voice signal when the voicesection information indicates the voice section, and enable acoefficient update signal when it is determined that the acoustic signalincludes the echo signal component; and an echo signal reductionprocessing unit configured to update a filter coefficient for setting adegree of suppression of the echo signal component from the acousticsignal according to the coefficient update signal, and generate, fromthe acoustic signal, a transmitting signal in which the echo signalcomponent is reduced. The filter coefficient update determination unitcalculates a feature value of the acoustic signal and enables thecoefficient update signal when a difference between a first featurevalue of a frequency band equal to or lower than the target frequencyand a second feature value of a frequency band higher than the targetfrequency is equal to or greater than a preset update determinationthreshold.

Accordingly, this embodiment provides a non-transitory computer readablemedium storing an echo cancellation program that suppresses an echosignal component corresponding to an output voice signal in an echocancellation device, the echo cancellation device including: a voiceoutput unit configured to output, to a space, the output voice signal inwhich frequency components equal to or higher than a predeterminedtarget frequency are suppressed, as a first voice signal; a voice inputunit configured to pick up a second voice signal propagating through thespace and generate an acoustic signal including a frequency componenthigher than the target frequency; and an operation unit configured toexecute a program, the echo cancellation program including: delayprocessing for delaying the output voice signal; voice section detectionprocessing for detecting that the output voice signal delayed by thedelay processing corresponds to a voice section including a voice signalcomponent, and generating voice section information; echo signalreduction processing for updating a filter coefficient for setting adegree of suppression of the echo signal component from the acousticsignal, and generating, from the acoustic signal, a transmitting signalin which the echo signal component is reduced; and filter coefficientupdate determination processing for determining whether or not theacoustic signal includes an echo signal component corresponding to theoutput voice signal when the voice section information indicates thevoice section, and updating the filter coefficient when it is determinedthat the acoustic signal includes the echo signal component. In thefilter coefficient update determination processing, a feature value ofthe acoustic signal is calculated and an instruction to update thefilter coefficient is sent when a difference between a first featurevalue of a frequency band equal to or lower than the target frequencyand a second feature value of a frequency band higher than the targetfrequency is equal to or greater than a preset update determinationthreshold.

Accordingly, this embodiment provides an echo cancellation method thatsuppresses an echo signal component corresponding to an output voicesignal in an echo cancellation device, the echo cancellation deviceincluding: a voice output unit configured to output, to a space, anoutput voice signal in which frequency components equal to or higherthan a predetermined target frequency are suppressed, as a first voicesignal; and a voice input unit configured to pick up a second voicesignal propagating through the space and generate an acoustic signalincluding a frequency component higher than the target frequency, theecho cancellation method including: delaying the output voice signal;detecting that the delayed output voice signal corresponds to a voicesection including a voice signal component and generating voice sectioninformation; updating a filter coefficient for setting a degree ofsuppression of the echo signal component from the acoustic signal, andgenerating, from the acoustic signal, a transmitting signal in which theecho signal component is reduced; calculating a feature value of theacoustic signal and calculating, as an echo signal determination value,a difference between a first feature value of a frequency band equal toor lower than the target frequency and a second feature value of afrequency band higher than the target frequency; and determining thatthe acoustic signal includes an echo signal component corresponding tothe output voice signal when the voice section information indicates thevoice section and the echo signal determination value is equal to orgreater than a preset update determination threshold, and sending aninstruction to update the filter coefficient.

According to this embodiment, an echo cancellation device, an echocancellation program, and an echo cancellation method which provide aneffect of suppressing a high echo signal are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram for explaining an installation state of ahands-free device to which an echo cancellation device according to afirst embodiment is applied;

FIG. 2 is a block diagram for explaining a call system including thehands-free device to which the echo cancellation device according to thefirst embodiment is applied;

FIG. 3 is a block diagram of the echo cancellation device according tothe first embodiment;

FIG. 4 is a flowchart for explaining an operation of the echocancellation device according to the first embodiment;

FIG. 5 is a graph for explaining features of a voice signal treated bythe echo cancellation device according to the first embodiment;

FIG. 6 is a graph for explaining features of a noise signal input to theecho cancellation device according to the first embodiment;

FIG. 7 is a graph for explaining a temporal waveform and a spectrogramof the voice signal treated by the echo cancellation device according tothe first embodiment;

FIG. 8 is a graph for explaining a spectrum of the voice signal treatedby the echo cancellation device according to the first embodiment;

FIG. 9 is a graph for explaining a temporal waveform and a spectrogramwhen a bandwidth control is performed on the voice signal treated by theecho cancellation device according to the first embodiment;

FIG. 10 is a graph for explaining a spectrum when a bandwidth control isperformed on the voice signal treated by the echo cancellation deviceaccording to the first embodiment;

FIG. 11 is a block diagram of an echo cancellation device according to asecond embodiment;

FIG. 12 is a graph for explaining a temporal waveform and a spectrogramof a voice signal on which echo cancellation processing is not performedby the echo cancellation device;

FIG. 13 is a graph for explaining a spectrum of the voice signal onwhich the echo cancellation processing is not performed by the echocancellation device;

FIG. 14 is a graph for explaining a temporal waveform and a spectrogramof a residual echo signal component of a voice signal on which the echocancellation processing is performed by the echo cancellation device;

FIG. 15 is a graph for explaining a spectrum of the residual echo signalcomponent of the voice signal on which the echo cancellation processingis performed by the echo cancellation device;

FIG. 16 is a block diagram of an echo cancellation device according to athird embodiment; and

FIG. 17 is a flowchart for explaining an operation of the echocancellation device according to the third embodiment.

DETAILED DESCRIPTION First Embodiment

Embodiments will be described below with reference to the drawings. Toclarify the explanation, omissions and simplifications are made asnecessary in the following description and the drawings. In thedrawings, the same elements are denoted by the same reference numerals,and repeated descriptions are omitted as needed.

Functional blocks described below are configured using hardware alone,software alone, or combinations thereof, and may be configured using apiece of hardware or software, or a plurality of pieces of hardware orsoftware. Each function (each processing) may be implemented by anoperation unit (e.g., a computer) including a CPU, a memory, and thelike. For example, programs for implementing a creation method in anembodiment are stored in a storage device and each function may beimplemented by causing the CPU to execute the programs stored in thestorage device.

These programs can be stored and provided to a computer using any typeof non-transitory computer readable media. Non-transitory computerreadable media include any type of tangible storage media. Examples ofnon-transitory computer readable media include magnetic storage media(such as floppy disks, magnetic tapes, hard disk drives, etc.), opticalmagnetic storage media (e.g., magneto-optical disks), CD-ROM (Read OnlyMemory), CD-R, CD-R/W, and semiconductor memories (such as mask ROM,PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (RandomAccess Memory), etc.). The program may be provided to a computer usingany type of transitory computer readable media. Examples of transitorycomputer readable media include electric signals, optical signals, andelectromagnetic waves. Transitory computer readable media can providethe program to a computer via a wired communication line, such aselectric wires and optical fibers, or a wireless communication line.

FIG. 1 shows a block diagram for explaining the configuration of ahands-free device including an echo cancellation device 1 according tothe first embodiment. The configuration shown in FIG. 1 is an exemplaryconfiguration of the hands-free device. The hands-free device may haveanother configuration, as long as the hands-free device includes aloudspeaker and a microphone. The example shown in FIG. 1 is an examplein which the hands-free device is provided in an automobile, but insteadthe hands-free device may be used at locations other than within anautomobile.

As shown in FIG. 1, the hands-free device is provided in an automobile.The hands-free device according to the first embodiment includes amicrophone provided in the body of the automobile (hereinafter referredto simply as a microphone), and a loudspeaker SP. The hands-free deviceaccording to the first embodiment uses the microphone as a voice inputunit and uses the loudspeaker SP as a voice output unit.

The hands-free device according to the first embodiment is used as avoice input/output interface, and makes a call with a call destinationusing a cellular phone or the like. In this regard, FIG. 2 shows a blockdiagram for explaining a call system including the hands-free deviceaccording to the first embodiment. As shown in FIG. 2, the hands-freedevice according to the first embodiment functions as a voice inputinterface for a cellular phone by transmitting a transmitting signal tothe cellular phone and receiving a received signal from the cellularphone. Assume that the echo cancellation device 1 according to the firstembodiment is provided in the hands-free device. Also assume that in thecall system according to the first embodiment, the cellular phone andthe echo cancellation device 1 treat voice signals at the same samplingrate. The echo cancellation device 1 according to the first embodimentwill be described in detail below.

FIG. 3 shows a block diagram of the echo cancellation device 1 accordingto the first embodiment. In the example shown in FIG. 3, assume that theecho cancellation device 1 treats the received signal and thetransmitting signal which are sampled at a sampling rate of 16 kHz.

As shown in FIG. 3, the echo cancellation device 1 according to thefirst embodiment includes a received signal input unit 11, atransmitting signal output unit 12, a voice output unit 13, a voiceinput unit 14, a delay processing unit 15, a voice section detectionprocessing unit 16, a filter coefficient update determination unit 17,an echo signal reduction processing unit 18, and a bandwidth controlunit 19.

The received signal input unit 11 receives the transmitting signalsupplied from an external device, and outputs the transmitting signal tothe inside of the received signal input unit. The bandwidth control unit19 performs bandwidth control processing on the transmitting signalsupplied from the received signal input unit 11 and outputs an outputvoice signal. The bandwidth control unit 19 is, for example, a lowpassfilter, and controls a frequency band equal to or higher than a targetfrequency of the received signal and generates the output voice signal.Assume herein that the target frequency is set in advance.

The voice output unit 13 outputs, to a space, an output voice signal S1,which is output from the bandwidth control unit 19, as a first voicesignal. The bandwidth of the output voice signal S1 output from thevoice output unit 13 is controlled so that the output voice signalincludes a frequency component equal to or lower than the targetfrequency. The first voice signal (for example, an echo signal shown inFIG. 3) is in a state where voice components equal to or higher than thetarget frequency are suppressed.

The voice input unit 14 picks up a second voice signal propagatingthrough the space, and generates an acoustic signal S2 including afrequency component higher than the target frequency. In this case, thesecond voice signal includes a voice component emitted from a speaker,road noise emitted from a noise source, and an echo signal componentoutput as the first voice signal.

The transmitting signal output unit 12 outputs, to the cellular phone,the transmitting signal generated after the echo cancellation processingis performed on the acoustic signal S2 in the echo signal reductionprocessing unit 18.

The delay processing unit 15 delays the output voice signal S1 andprovides the voice section detection processing unit 16 with the delayedsignal. In this case, the amount of delay of the output voice signal S1that is delayed by the delay processing unit 15 is a time correspondingto a total delay time when the first voice signal which is output fromthe voice output unit 13 and is changed through a space propagationcoefficient of a cabin space into an echo signal is picked up as asignal included in the second voice signal.

The voice section detection processing unit 16 detects that the outputvoice signal Si delayed by the delay processing unit 15 corresponds to avoice section including a voice signal component, and generates voicesection information. This voice section information is supplied to thefilter coefficient update determination unit 17. In this case, the voicesection detection processing unit 16 confirms whether or not a signalhaving an amplitude level exceeding a preset threshold is present in acertain time interval in the output voice signal S1, thereby detectingthe presence or absence of a voice section. For example, in a case wherethe time interval is set to 5 msec and the threshold is set to −24 dB,the absolute value of the amplitude level of the output voice signal S1which is delayed by the delay processing unit 15 is confirmed. When anamplitude level exceeding −24 dB is detected, it is determined that theoutput voice signal corresponds to the voice section, and when theamplitude level is lower than −24 dB, it is determined that the outputvoice signal does not correspond to the voice section.

When the voice section information indicates the voice section, thefilter coefficient update determination unit 17 determines whether ornot the acoustic signal includes an echo signal component correspondingto the output voice signal S1. When it is determined that the acousticsignal includes the echo signal component, a coefficient update signalS3 is enabled. In this case, the filter coefficient update determinationunit 17 calculates a feature value of the acoustic signal, and when adifference between a first feature value of a frequency band equal to orlower than the target frequency and a second feature value of afrequency band higher than the target frequency is equal to or greaterthan a preset update determination threshold, the filter coefficientupdate determination unit 17 enables the coefficient update signal S3.

The filter coefficient update determination unit 17 includes an echopath estimation processing determination unit 21, a feature valuedetection processing unit 22, and a frequency signal conversionprocessing unit 23. The frequency signal conversion processing unit 23converts the acoustic signal S2 into a frequency signal. Morespecifically, the frequency signal conversion processing unit 23converts the acoustic signal S2 from a time domain signal to a frequencydomain signal by FFT (Fast Fourier Transform) or DCT (discrete cosinetransform). Further, the frequency signal conversion processing unit 23converts the acoustic signal S2 into a frequency signal at a samplingrate (for example, 16 kHz) at which a voice of a frequency band higherthan the target frequency can be recorded.

For example, when the sampling rate is 16 kHz and the number of samplesfor frequency signal conversion processing to 1024 samples, thefrequency signal conversion processing unit 23 obtains a frequencyresolution of 15.625 Hz by Formula (1).

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack & \; \\{{{frequency}\mspace{14mu} {resolution}} = {\frac{{sampling}\mspace{14mu} {rate}}{{number}\mspace{14mu} {of}\mspace{14mu} {samples}}\lbrack{Hz}\rbrack}} & (1)\end{matrix}$

In this case, a period of a frequency conversion cycle is calculated as0.032 sec by Formula (2).

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack & \; \\{{{frequency}\mspace{14mu} {conversion}\mspace{14mu} {cycle}} = {\left( \frac{1}{{sampling}\mspace{14mu} {rate}} \right) \times {\left( \frac{{number}\mspace{14mu} {of}\mspace{14mu} {samples}}{2} \right)\left\lbrack \sec \right\rbrack}}} & (2)\end{matrix}$

The feature value detection processing unit 22 calculates the firstfeature value and the second feature value from the frequency signalobtained through the conversion by the frequency conversion processingunit. More specifically, the feature value detection processing unit 22detects the feature value of a spectrum from the spectrum signal of theacoustic signal S2 which is converted into a frequency domain signal. Asa method for detecting the feature value of the echo spectrum, aspectrum intensity in a wide frequency band of the acoustic signal S2 isdetected. A specific detection method is described later.

Further, the feature value detection processing unit 22 also detects aspeaker spectrum signal obtained from a speaker's voice in the cabin ofthe automobile. Examples of the method for detecting the feature valueof the speaker spectrum include a method of monitoring a time change ofthe spectrum intensity in the frequency band which is equal to or higherthan the target frequency and in which the voice spectrum intensity canbe detected.

The echo path estimation processing determination unit 21 determineswhether or not to execute echo path estimation processing by using thevoice section information output from the voice section detectionprocessing unit 16 and spectrum feature value detection informationoutput from the feature value detection processing unit 22. Morespecifically, when the voice section information indicates the voicesection and the difference between the first feature value and thesecond feature value is equal to or greater than the preset updatedetermination threshold, the coefficient update signal S3 is enabled. Asthe spectrum feature value detection information output from the featurevalue detection processing unit 22, the spectrum feature value detectioninformation of the target frequency band calculated by the feature valuedetection processing unit 22 when the voice section informationindicates the voice section is used by using the voice sectioninformation so as to prevent an erroneous detection due to the effect ofnoise in the cabin of the automobile. When it is determined that thespectrum feature value detection information of the target frequencyband exceeds the threshold, it is determined that the echo signal isincluded in the acoustic signal, and a notification is sent to anadaptive filter unit 31 of the echo signal reduction processing unit 18to execute the echo path estimation processing. However, if the echoestimation processing is executed when the echo signal is included inthe acoustic signal and the speaker speaks in the cabin of theautomobile, that is, in a so-called double-talk state, an error occursin updating of the adaptive filter coefficient, which leads todeterioration in the effect of echo cancellation. Therefore, in thedouble-talk state, a notification is sent to the adaptive filter unit 21so as to prevent the adaptive filter unit from executing the echoestimation processing.

The echo signal reduction processing unit 18 updates the filtercoefficient for setting the degree of suppression of the echo signalcomponent corresponding to the output voice signal from the acousticsignal S2 according to the coefficient update signal S2, and generates,from the acoustic signal S2, the transmitting signal in which the echosignal component is reduced. The echo signal reduction processing unit18 includes the adaptive filter unit 31 and an adder 32.

The adaptive filter unit 31 updates the filter coefficient according tothe coefficient update signal S3, and generates a pseudo echo signalbased on the output voice signal S1 delayed by the delay processing unitdelay processing unit 15 and the transmitting signal output from theaddition unit 32. The adaptive filter unit 31 may have a filter lengthof about 300 Taps in, for example, an LMS (Least Mean Square) algorithm.In the adaptive filter unit 31, the output voice signal S1 delayed bythe delay processing unit 15 is used as a reference signal. Further, inthe adaptive filter unit 31, a residual echo signal, which is obtainedafter addition processing is performed by the adder 32, is used as anerror signal. The adaptive filter unit 31 updates the coefficient of theadaptive filter when the echo path estimation processing determinationunit 21 makes a determination to execute the echo path estimationprocessing (for example, when the coefficient update signal S3 isenabled).

The adder 32 subtracts the pseudo echo signal component output from theadaptive filter unit 31 from the acoustic signal S2 and outputs thetransmitting signal.

Next, an operation of the echo cancellation device 1 according to thefirst embodiment will be described. In the following description, inparticular, the echo cancellation processing in the echo cancellationdevice 1 will be described. In this regard, FIG. 4 shows a flowchart forexplaining an operation of the echo cancellation device 1 according tothe first embodiment.

As shown in FIG. 4, when the echo cancellation device 1 according to thefirst embodiment starts the echo cancellation processing, the filtercoefficient update determination unit 17 first acquires the voicesection information of the output voice signal S1 (step S11). Further,the filter coefficient update determination unit 17 determines whetheror not the output voice signal S1 includes a voice signal (step S12). Inthis step S12, when it is determined that the voice section informationindicates a non-voice section (a branch of NO in step S12), the acousticsignal S2 does not include the echo component. Accordingly, the echocancellation device 1 terminates the echo cancellation processingwithout executing the echo cancellation processing.

On the other hand, in step S12, when it is determined that the voicesection information indicates the voice section (a branch of YES in stepS12), the frequency signal conversion processing unit 23 performs thefrequency conversion processing on the acoustic signal S2 (step S13).After that, the feature value detection processing unit 22 performsfeature value extraction processing in a high-frequency band (step S14).Further, the echo path estimation processing determination unit 21performs processing for detecting the presence or absence of the echosignal (step S15).

In the echo signal detection processing in step S15, when the echosignal is not detected (a branch of NO in step S15), the echocancellation device 1 terminates the echo cancellation processingwithout executing the echo cancellation processing. On the other hand,in the echo signal detection processing in step S15, when the echosignal is detected (a branch of YES in step S15), the adaptive filterunit 31 performs the echo path estimation processing (step S16), andalso performs pseudo echo signal generation processing (step S17).Further, the adder 32 performs echo signal removal processing (stepS18).

The feature value extraction processing in step S14 and step S15 will bedescribed in more detail by providing a specific example of the acousticsignal S2. FIG. 5 shows a graph for explaining features of a voicesignal input as the acoustic signal S2. The example of FIG. 5 shows awaveform of a voice signal obtained by recording only a voice in a quietroom. In FIG. 5, an upper graph shows a time signal waveform of thevoice signal, and a lower graph shows a spectrogram of the voice signal.Note that in FIG. 5, in the (upper) graph showing the temporal waveform,the horizontal axis represents time and the vertical axis represents anamplitude, and in the (lower) graph showing the spectrogram, thehorizontal axis represents time; the vertical axis represents afrequency; and the spectrum intensity of the signal is represented bygrayscale.

As shown in FIG. 5, in the voice spectrum, the frequency band indicatinga high spectrum intensity of a consonant is different from that of avowel. The spectrum intensity of a vowel tends to be high in a range of10 to 4000 Hz, and tends to be low in a range of 4000 Hz to 8000 Hz. Thespectrum intensity of a consonant tends to be high in a range of 3000 Hzto 9000 Hz, and tends to be low in a range of 9000 Hz to 15000 Hz.

FIG. 6 shows a graph for explaining features of a noise signal input tothe echo cancellation device 1 according to the first embodiment. Thegraph of FIG. 6 shows a spectrum signal of road noise picked up in theautomobile traveling on an expressway. In the graph of FIG. 6, thehorizontal axis represents a frequency and the vertical axis representsthe signal intensity of road noise.

As shown in FIG. 6, the road noise has a strong spectrum in a range of20 to 1500 Hz. In particular, the road noise has an extremely strongspectrum in a low frequency range of 500 Hz or lower. In other words,the road noise has little effect on the voice signal in a frequency bandof 2000 Hz or higher.

Next, FIG. 7 shows a graph for explaining a temporal waveform and aspectrogram of the voice signal treated by the echo cancellation device1 according to the first embodiment. FIG. 8 shows a graph for explaininga spectrum of the voice signal treated by the echo cancellation deviceaccording to the first embodiment. The examples of FIGS. 7 and 8 showthe voice signal which has a waveform obtained with a sampling rate of16 kHz and on which the bandwidth control processing is not performed bythe bandwidth control unit 19. As shown in FIGS. 7 and 8, when thesampling rate is 16 kHz, the reproduction frequency band of the voicesignal is up to about 8 kHz.

FIGS. 9 and 10 show graphs for explaining features of a voice signalwhen the bandwidth control processing is performed on the voice signalshown in FIGS. 7 and 8. In the examples shown in FIGS. 9 and 10, thetarget frequency is set to 4 kHz and the bandwidth control unit 19attenuates signal components in a frequency band of 4 kHz or higher. Asshown in FIGS. 9 and 10, when the bandwidth control using the targetfrequency (for example, 4 kHz) as an upper limit is performed, almostall the voice components in the frequency band equal to or higher thanthe target frequency are removed.

In the echo cancellation device 1 according to the first embodiment, thevoice input unit 14 and the frequency signal conversion processing unit23 which are capable of acquiring the acoustic signal S2 having thefeatures shown in FIGS. 7 and 8 acquire the acoustic signal S2 includingthe echo signal having the features shown in FIGS. 9 and 10. Further,the echo cancellation device 1 according to the first embodimentdetermines whether or not the echo signal is present based on theacoustic signal S2 including the echo signal having the features shownin FIGS. 9 and 10. In this regard, the processing in the feature valuedetection processing unit 22 and the echo path estimation processingdetermination unit 21 will be described by providing a specific exampleof numerical values.

First, when the voice input unit 14 generates the acoustic signal S2 ata sampling rate of 16 kHz, and the frequency signal conversionprocessing unit 23 performs frequency conversion processing with thenumber of samples of 1024 samples and at a frequency resolution of15.625 Hz. When the target frequency at which the bandwidth of theoutput voice signal S1 is controlled is set to 4 kHz, the frequencysignal corresponding to the target frequency is the 256th spectrumsignal. Accordingly, the feature value detection processing unit 22calculates, as the first feature value, the average value of theintensities of the 240th to 256th spectrum signals which are frequencysignals of 3750 Hz. Further, the feature value detection processing unit22 calculates, as the second feature value, the average value of theintensities of the 256th to 262th spectrum signals. The 272th spectrumsignal is a frequency signal of 4250 Hz. In the feature value detectionprocessing of step S14, the feature value detection processing unit 22calculates the feature values described above.

Further, in the echo signal detection processing of step S15, the echopath estimation processing determination unit 21 determines whether ornot the echo signal is present on the basis of whether or not thedifference between the first feature value and the second feature valueexceeds the preset update determination threshold (for example, 12 dB).Specifically, when the difference between the first feature value andthe second feature value is smaller than the update determinationthreshold, it is determined that the echo signal is not present and theecho path estimation processing determination unit 21 disables thecoefficient update signal S3. When the difference between the firstfeature value and the second feature value is equal to or greater thanthe update determination threshold, it is determined that the echosignal is present and the echo path estimation processing determinationunit 21 enables the coefficient update signal S3.

In this case, the echo path estimation processing determination unit 21according to the first embodiment calculates the feature value of theacoustic signal S2 and detects the speaker spectrum signal obtained froma voice emitted from the speaker. A method for detecting the speakerspectrum signal will be described below.

For example, when the sampling rate of the hands-free communicationdevice 1 is set to 16 kHz; the target frequency is set to 4 kHz; and theframe size for frequency conversion processing is set to 1024 samples,the frequency resolution is 15.625 Hz; a time per frame is 32 msec; andthe frequency that can be picked up by the microphone is 8 kHz. In thespectrum signal, the spectrum signal corresponding to the targetfrequency of 4 kHz is the 256th spectrum signal. In the detection of thespeaker spectrum signal, the feature value detection processing unit 22calculates the spectrum intensities of 256 spectrum signals, i.e., the256th to 512th spectrum signals, assuming that the upper limit of thevoice bandwidth is the maximum frequency of 8 kHz of the 512th signal.The echo path estimation processing determination unit 21 compares thespectrum intensity of the speaker spectrum signal in the present framewith that in the previous frame, thereby detecting the voice section ofthe speaker. When the present frame corresponds to the voice section,the echo path estimation processing determination unit 21 maintains thecoefficient update signal S3 in the disabled state, thereby interruptingupdating of the filter coefficient of the adaptive filter unit 31.

In the case of a system in which the sampling rate of the hands-freecommunication device 1 sufficiently exceeds the frequency band of ahuman voice, an upper limit to a frequency band to be detected may beset. For example, when the sampling rate of the hands-free communicationdevice 1 is 64 kHz; the target frequency is 4 kHz; and the frame sizefor frequency conversion processing is 4096 samples, the frequencyresolution is 15.625 Hz; a time per frame is 32 msec; and the frequencythat can be picked up by the microphone is 32 kHz. The spectrum signalcorresponding to the target frequency of 4 kHz is the 256th spectrumsignal. In this case, the upper limit of the voice bandwidth detected bythe feature value detection processing unit 22 is 10 kHz of the 640thsignal. Further, the feature value detection processing unit 22calculates the intensities of 384 spectrum signals, i.e., the 256th to640th spectrum signals. The echo path estimation processingdetermination unit 21 compares the spectrum intensity in the presentframe with the spectrum intensity in the previous frame, therebydetecting the voice section of the speaker.

In order to compare the spectrum intensities, it is determined whetherthe spectrum in the present frame exceeds a certain threshold (forexample, 12 dB) with respect to the spectrum in the previous frame.Further, it is determined whether there is a speaker's voice in thecabin of the automobile on the basis of whether or not the number ofspectrum signals exceeding the threshold exceeds a certain threshold(for example, 100 [signals]). The spectrum signal in the previous framecan be updated by the following Formula (3). Note that in Formula (3), irepresents the spectrum number.

[Formula 3]

Previous spectrum [i]=(previous spectrum [i]×0.99)+(present spectrum[i]×0.01)    (3)

As described above, the echo cancellation device 1 according to thefirst embodiment outputs the output voice signal S1 whose bandwidth iscontrolled with the target frequency lower than the frequency band thatcan be picked up, and compares the first feature value of the acousticsignal S2 having the predetermined frequency band equal to or lower thanthe target frequency of the acoustic signal S2 generated from thecollected voice with the second feature value of the acoustic signal S2having the predetermined frequency band higher than the targetfrequency, thereby detecting the presence or absence of the echo signal.Thus, the echo cancellation device 1 according to the first embodimentcan detect the presence or absence of the echo signal with highaccuracy.

The echo cancellation device according to the first embodiment limitsthe frequency band of the spectrum signal used for calculation of thefirst feature value and the second feature value to the vicinity of thetarget frequency. Consequently, the echo cancellation device 1 accordingto the first embodiment can reduce the amount of memory used fordetecting the echo signal. By limiting the frequency band of thespectrum signal used for calculation of the first feature value and thesecond feature value to the vicinity of the target frequency, the echocancellation device 1 according to the first embodiment can detect thepresence or absence of the echo signal without being affected by roadnoise or the like.

Furthermore, the echo cancellation device 1 according to the firstembodiment calculates the first feature value and the second featurevalue and detects whether or not the spectrum signal of the acousticsignal S2 having a frequency band higher than the target frequencyincludes the speaker spectrum of a voice emitted from the speaker. Whenthe echo cancellation device 1 according to the first embodimentdetermines that the acoustic signal S2 corresponds to the voice sectionincluding the speaker spectrum, the echo cancellation device 1interrupts updating of the filter coefficient of the adaptive filterunit 31. Thus, the echo cancellation device 1 according to the firstembodiment can prevent erroneous updating of the filter coefficient dueto a voice emitted from the speaker and enhance the effect of echocancellation.

Second Embodiment

In a second embodiment, another mode of the method for controlling thefrequency band of the output voice signal S1 will be described. In thisregard, FIG. 11 shows a block diagram of an echo cancellation device 2according to the second embodiment. As shown in FIG. 11, the echocancellation device 2 according to the second embodiment has aconfiguration in which the bandwidth control unit 19 is omitted from theconfiguration of the echo cancellation device 1 according to the firstembodiment.

The echo cancellation device 2 according to the second embodimentgenerates the acoustic signal S2 at a sampling rate higher than that ofthe received signal received from a cellular phone or the like, andgenerates a transmitting signal from the acoustic signal S2. Thus, theecho cancellation device 2 according to the second embodiment controlsthe frequency band of the output voice signal S1 to be lower than thefrequency band of the acoustic signal S2.

Specifically, for example, when the sampling rate of the received signalis 8 kHz, the frequency band of the output voice signal S1 is controlledto 4 kHz. On the other hand, when the sampling rate of the acousticsignal S2 is 16 kHz, the frequency band of the acoustic signal S2 is 8kHz. Accordingly, in the second embodiment, the signal characteristic ofthe echo signal generated from the output voice signal S1 can be set tobe the same as the signal characteristic of the signal whose frequencyband is controlled as shown in FIGS. 9 and 10, and the signalcharacteristic of the acoustic signal S2 can be set to be the same asthe signal characteristic of the signal whose bandwidth is notcontrolled as shown in FIGS. 7 and 8. In other words, in the echocancellation device 2 according to the second embodiment, the echocancellation device 2 is operated at a sampling rate higher than thesampling rate of the transmitting signal, thereby making it possible tocarry out the detection of the echo signal and the echo cancellationprocessing that are similar to those of the echo cancellation device 1according to the first embodiment.

Note that a human voice signal has a feature that the basic frequency ofthe voice signal has a strong spectrum of about 100 to 250 Hz, althoughit varies from person to person and between men and women, and thespectrum intensity gradually decreases as the frequency band increasestwo-fold, three-fold, four-fold, . . . , and n-fold according to theharmonic structure based on the basic frequency. In the human voicesignal, a spectrum signal is present in about 10 to 12 kHz.

As described above, the echo cancellation device 2 according to thesecond embodiment can carry out the detection of the echo signal and theecho cancellation processing that are similar to those of the echocancellation device 1 according to the first embodiment, without usingthe bandwidth control unit 19.

Third Embodiment

A third embodiment illustrates an example in which residual echocancellation processing for removing residual echo signal componentsremaining in the transmitting signal after echo cancellation processingis performed once is added to the processing of the echo cancellationdevice 1 according to the first embodiment. First, the residual echosignal components will be described.

FIGS. 12 and 13 show graphs for explaining features of a voice signal onwhich the echo cancellation processing is not performed by the echocancellation device. FIG. 12 is a graph for explaining a temporalwaveform and a spectrogram of the voice signal. FIG. 13 is a graph forexplaining a spectrum of the voice signal. FIGS. 14 and 15 are graphsfor explaining residual echo signal components of the voice signal afterthe echo cancellation device performs the echo cancellation processing.FIG. 14 is a graph for explaining a temporal waveform and a spectrogramof the residual echo signal components. FIG. 15 is a graph forexplaining a spectrum of the residual echo signal components.

Even in the case where the echo cancellation processing described in thefirst and second embodiments is performed, if the filter coefficient ofthe adaptive filter unit 31 includes an error, the echo signal cannot becompletely cancelled due to the pseudo echo signal generated by theadaptive filter unit 31. In this case, the residual echo signalcomponents shown in FIGS. 14 and 15 remain in the voice signal shown inFIGS. 12 and 13. The echo cancellation device 3 according to the thirdembodiment removes the residual echo signal components.

FIG. 16 shows a block diagram of the echo cancellation device 3according to the third embodiment. As shown in FIG. 16, the echocancellation device 3 according to the third embodiment has aconfiguration in which a residual echo signal suppressing unit 41 isincorporated between the echo signal reduction processing unit 18 andthe transmitting signal output unit 12 of the echo cancellation device 1according to the first embodiment.

The residual echo signal suppressing unit 41 receives, as a firsttransmitting signal, the transmitting signal output from the echo signalreduction processing unit 18, suppresses residual echo signal componentsincluded in the first transmitting signal, and outputs the resultantsignal as a second transmitting signal. The residual echo signalsuppressing unit 41 includes a frequency signal conversion processingunit 42, a residual echo signal attenuation processing determinationunit 43, a residual echo signal suppression processing unit 44, and atime signal conversion processing unit 45. Note that the frequencysignal conversion processing unit 42 and a feature value detectionprocessing unit 52 in the residual echo signal attenuation processingdetermination unit 43 are blocks similar to the frequency signalconversion processing unit 23 and the feature value detection processingunit 22, respectively. Referring to FIG. 16, the feature value detectionprocessing unit 22 serves as a first feature value detection processingunit; the frequency signal conversion processing unit 23 serves as afirst frequency signal conversion processing unit; the frequency signalconversion processing unit 42 serves as a second frequency signalconversion processing unit; and the feature value detection processingunit 52 serves as a second feature value detection processing unit.

The frequency signal conversion processing unit 42 converts the firsttransmitting signal, which is subjected to the echo cancellationprocessing and output from the adder 32, from a time domain signal intoa frequency domain signal (frequency signal). The frequency signalconversion processing unit 42 converts the first transmitting signalinto a frequency signal by FFT or DCT.

The residual echo signal attenuation processing determination unit 43determines whether or not a residual echo signal is present anddetermines whether or not to execute residual echo signal suppressionprocessing. Accordingly, the residual echo signal attenuation processingdetermination unit 43 includes an echo path estimation processingdetermination unit 51 and the feature value detection processing unit52.

The feature value detection processing unit 52 detects a feature valueof a residual echo spectrum. As a method for calculating the featurevalue of the residual echo spectrum in the feature value detectionprocessing unit 52, a method similar to the spectrum calculation methodof the feature value detection processing unit 22 can be employed.

When the echo path estimation processing determination unit 51determines that residual echo signal components are present based on thedetected information about the residual echo spectrum that is detectedby the feature value detection processing unit 52, the echo pathestimation processing determination unit 51 instructs the residual echosignal suppression processing unit 44 to carry out the residual echosignal suppression processing.

The residual echo signal suppression processing unit 44 carries outstationary spectrum estimation processing, residual echo spectrumestimation processing, and residual echo spectrum suppressionprocessing. In the stationary spectrum estimation processing, theinformation about the stationary spectrum intensity is updated whenthere is no residual echo and no voice is emitted from the speaker. Thestationary spectrum information is updated by Formula (4). Note that inFormula (4), i represents the spectrum number.

[Formula 4]

Stationary spectrum [i]=(stationary spectrum [i]×0.99)+(present spectrum[i]×0.01)    (4)

In the residual echo spectrum estimation processing, residual echosignal components are detected, and when no voice is emitted from thespeaker, the information about the remaining spectrum intensity isupdated. The remaining spectrum information is updated by Formula (5).Note that in Formula (5), i represents the spectrum number.

[Formula 5]

Residual spectrum [i]=(residual spectrum [i]×0.99)+(present spectrum[i]×0.01)    (5)

In the residual echo spectrum suppression processing, the differencebetween the residual echo spectrum and the stationary echo spectrum issubtracted from the present spectrum signal, thereby suppressing theresidual echo signal. A method for suppressing the residual echospectrum is obtained by Formulas (6) and (7). Note that in Formula (6)and Formula (7), i represents the spectrum number.

[Formula 6]

Spectrum suppression amount [i]=(residual spectrum [i])−(stationaryspectrum [i])    (6)

[Formula 7]

Suppressed spectrum [i]=(present spectrum [i])−(spectrum suppressionamount [i])    (7)

The time signal conversion processing unit 45 performs frequency inversetransform processing for transforming the spectrum signal in whichresidual echo signal components are suppressed from a frequency domainto a time domain, thereby generating the second transmitting signal.

Next, the operation of residual echo signal component suppressionprocessing of the echo cancellation device 3 according to the thirdembodiment will be described with reference to the flowchart shown inFIG. 17. As shown in FIG. 17, in the echo cancellation device 3according to the third embodiment, when the residual echo suppressionprocessing is started, the frequency conversion processing (step S21) isperformed by the frequency signal conversion processing unit 42 and thefeature value extraction processing (step S22) in a high-frequency bandis performed by the feature value detection processing unit 52.

Further, in the echo cancellation device 3, the echo path estimationprocessing determination unit 51 detects the residual echo signal basedon the feature value extracted in step S22 (step S23). In this step S23,when it is determined that there are residual echo signal components (abranch of YES in step S23), the echo path estimation processingdetermination unit 51 detects the presence or absence of the voicesignal (step S26). On the other hand, in step S23, also when it isdetermined that there are no residual echo signal components (a branchof NO in step S23), the echo path estimation processing determinationunit 51 detects the presence or absence of the voice signal (step S24).

In step S24, when the voice signal is detected (a branch of YES in stepS24), the echo cancellation device 3 performs time signal conversionprocessing on the first transmitting signal (step S29), withoutperforming the echo signal suppression processing, and terminates theresidual echo suppression processing. On the other hand, in step S24,when the voice signal is not detected (a branch of NO in step S24), theresidual echo signal suppression processing unit 44 performs thestationary spectrum estimation processing (step S25) and then performsthe time signal conversion processing on the first transmitting signal(step S29) and terminates the residual echo suppression processing.

In step S26, when the voice signal is detected (a branch of YES in stepS27), the residual echo signal suppression processing unit 44 performsthe residual echo spectrum suppression processing (step S28), and thenperforms the time signal conversion processing on the first transmittingsignal subjected to the residual echo spectrum suppression processing(step S29), and terminates the residual echo suppression processing. Onthe other hand, in step S26, when the voice signal is not detected (abranch of NO in step S26), the residual echo signal suppressionprocessing unit 44 performs the residual echo spectrum estimationprocessing (step S27) and then performs the residual echo spectrumsuppression processing (step S28). After that, the echo cancellationdevice 3 performs the time signal conversion processing on the firsttransmitting signal subjected to the residual echo spectrum suppressionprocessing (step S29), and terminates the residual echo suppressionprocessing.

As described above, the echo cancellation device 3 according to thethird embodiment performs suppression processing on the echo signalcomponents remaining after the echo cancellation processing.Consequently, the echo cancellation device 3 according to the thirdembodiment provides an echo cancellation effect higher than that of theecho cancellation device 1 according to the first embodiment.

Note that this embodiment is not limited to the above embodiments, andcan be modified as appropriate without departing from the scope of theinvention.

1. An echo cancellation device comprising: a voice output unitconfigured to output, to a space, an output voice signal in whichfrequency components equal to or higher than a predetermined targetfrequency are suppressed, as a first voice signal; a voice input unitconfigured to pick up a second voice signal propagating through thespace and generate an acoustic signal including a frequency componenthigher than the target frequency; a delay processing unit configured todelay the output voice signal; a voice section detection processing unitconfigured to detect that the output voice signal delayed by the delayprocessing unit corresponds to a voice section including a voice signalcomponent, and generate voice section information; a filter coefficientupdate determination unit configured to determine whether or not theacoustic signal includes an echo signal component corresponding to theoutput voice signal when the voice section information indicates thevoice section, and enable a coefficient update signal when it isdetermined that the acoustic signal includes the echo signal component;and an echo signal reduction processing unit configured to update afilter coefficient for setting a degree of suppression of the echosignal component from the acoustic signal according to the coefficientupdate signal, and generate, from the acoustic signal, a transmittingsignal in which the echo signal component is reduced, wherein the filtercoefficient update determination unit calculates a feature value of theacoustic signal and enables the coefficient update signal when adifference between a first feature value of a frequency band equal to orlower than the target frequency and a second feature value of afrequency band higher than the target frequency is equal to or greaterthan a preset update determination threshold.
 2. The echo cancellationdevice according to claim 1, further comprising a bandwidth control unitconfigured to generate the output voice signal by controlling abandwidth of a frequency equal to or higher than the target frequency ofa received signal externally received, and output the generated outputvoice signal to the voice output unit and the delay processing unit. 3.The echo cancellation device according to claim 1, wherein the outputvoice signal is a signal with a sampling rate lower than that of theacoustic signal.
 4. The echo cancellation device according to claim 1,wherein the filter coefficient update determination unit disables thecoefficient update signal when the voice section information indicatesthe voice section and the acoustic signal includes a voice component ofa speaker.
 5. The echo cancellation device according to claim 1, whereinthe filter coefficient update determination unit includes: a frequencysignal conversion processing unit configured to convert the acousticsignal into a frequency signal; a feature value detection processingunit configured to calculate the first feature value and the secondfeature value from the frequency signal obtained through the conversionby the frequency signal conversion processing unit; and an echo pathestimation processing determination unit configured to enable thecoefficient update signal when the voice section information indicatesthe voice section and a difference between the first feature value andthe second feature value is equal to or greater than a preset updatedetermination threshold.
 6. The echo cancellation device according toclaim 1, wherein the echo signal reduction processing unit includes anadaptive filter unit and an addition unit, the adaptive filter unitupdates the filter coefficient according to the coefficient updatesignal and generates a pseudo echo signal based on the output voicesignal delayed by the delay processing unit and a transmitting signaloutput from the addition unit, and the addition unit subtracts thepseudo echo signal from the acoustic signal and outputs the transmittingsignal.
 7. The echo cancellation device according to claim 1, furthercomprising a residual echo signal suppressing unit configured to receivethe transmitting signal as a first transmitting signal, suppress aresidual echo signal component included in the first transmittingsignal, and output a resultant signal as a second transmitting signal.8. A non-transitory computer readable medium storing an echocancellation program that suppresses an echo signal componentcorresponding to an output voice signal in an echo cancellation device,the echo cancellation device comprising: a voice output unit configuredto output, to a space, the output voice signal in which frequencycomponents equal to or higher than a predetermined target frequency aresuppressed, as a first voice signal; a voice input unit configured topick up a second voice signal propagating through the space and generatean acoustic signal including a frequency component higher than thetarget frequency; and an operation unit configured to execute a program,the echo cancellation program comprising: delay processing for delayingthe output voice signal; voice section detection processing fordetecting that the output voice signal delayed by the delay processingcorresponds to a voice section including a voice signal component, andgenerating voice section information; echo signal reduction processingfor updating a filter coefficient for setting a degree of suppression ofthe echo signal component from the acoustic signal, and generating, fromthe acoustic signal, a transmitting signal in which the echo signalcomponent is reduced; and filter coefficient update determinationprocessing for determining whether or not the acoustic signal includesan echo signal component corresponding to the output voice signal whenthe voice section information indicates the voice section, and updatingthe filter coefficient when it is determined that the acoustic signalincludes the echo signal component, wherein in the filter coefficientupdate determination processing, a feature value of the acoustic signalis calculated and an instruction to update the filter coefficient issent when a difference between a first feature value of a frequency bandequal to or lower than the target frequency and a second feature valueof a frequency band higher than the target frequency is equal to orgreater than a preset update determination threshold.
 9. An echocancellation method that suppresses an echo signal componentcorresponding to an output voice signal in an echo cancellation device,the echo cancellation device comprising: a voice output unit configuredto output, to a space, an output voice signal in which frequencycomponents equal to or higher than a predetermined target frequency aresuppressed, as a first voice signal; and a voice input unit configuredto pick up a second voice signal propagating through the space andgenerate an acoustic signal including a frequency component higher thanthe target frequency, the echo cancellation method comprising: delayingthe output voice signal; detecting that the delayed output voice signalcorresponds to a voice section including a voice signal component andgenerating voice section information; updating a filter coefficient forsetting a degree of suppression of the echo signal component from theacoustic signal, and generating, from the acoustic signal, atransmitting signal in which the echo signal component is reduced;calculating a feature value of the acoustic signal and calculating, asan echo signal determination value, a difference between a first featurevalue of a frequency band equal to or lower than the target frequencyand a second feature value of a frequency band higher than the targetfrequency; and determining that the acoustic signal includes an echosignal component corresponding to the output voice signal when the voicesection information indicates the voice section and the echo signaldetermination value is equal to or greater than a preset updatedetermination threshold, and sending an instruction to update the filtercoefficient.